Probabilistic optimization of the dose coverage – applied to radiotherapy treatment planning of cervical cancer
(English)Manuscript (preprint) (Other academic)
Probabilistic (or robust) optimization is an alternative to margins for handling geometrical uncertainties in treatment planning of radiotherapy where the uncertainties are explicitly incorporated in the optimization through sampling of treatment scenarios. We present a probabilistic method based on statistical measures close to those behind conventional margin based planning. The dose planner requests a dose coverage to a specified probability, which the algorithm then attempts to fulfil.
We define the Percentile UnderDosage (PUD) as a measure of the target minimum dose coverage probability, i.e. the dose coverage that a treatment plan meet or exceed to a given probability. Margin based planning commonly use the implicit probabilistic treatment criteria that the 90th PUD is at least 95% of the intended dose. For optimization we use the Expected Percentile UnderDosage (EPUD) defined as the average dose coverage below a given PUD. The EPUD is, in contrast to PUD, a convex measure and hence standard optimization techniques can be used to find the optimal treatment plan. We propose an iterative method where a treatment optimization is performed at each iteration and the EPUD tolerance is adjusted gradually until a desired PUD is met.
We demonstrate our proposed probabilistic planning method for cervical cancer patients. The uncertainty caused by organ deformation is explicitly included in the probabilistic optimization where a statistical shape model is used to sample scenarios with different deformations. For all patients in this work, the iterative process of finding the EPUD tolerance converged in less than 10 iterations to within 0.1Gy of the requested PUD even though a conservative update scheme was used. The resulting estimated PUD was validated based on 1000 simulated scenarios not part of the optimization yielding an agreement within 1.2% of the requested PUD.
Other Physics Topics
Research subject Medical Radiophysics
IdentifiersURN: urn:nbn:se:uu:diva-304982OAI: oai:DiVA.org:uu-304982DiVA: diva2:1034218